This invention relates to compression relief engine retarders, and more particularly to slave pistons in these systems that incorporate a clipping mechanism to limit their maximum displacement.
Engine retarders of the compression relief type are well known in the art. In general, such retarders are designed temporarily to convert an internal combustion engine into an air compressor so as to develop a retarding horsepower which may be a substantial portion of the operating horsepower developed by the engine in its operating mode.
The basic design for an engine retarding system of the type here involved is disclosed in Cummins U.S. Pat. No. 3,220,392. In that design a hydraulic system (which may make use of oil from the associated engine) is employed wherein the motion of a master piston actuated by an appropriate intake, exhaust, or fuel injector pushtube or rocker arm controls the motion of a slave piston. The slave piston opens the exhaust valve of a cylinder of the internal combustion engine near the end of the compression stroke whereby the work done in compressing the air in that cylinder is not recovered during the subsequent expansion or "power" stroke but, instead, is dissipated through the exhaust and cooling systems of the engine.
In this type of retarder it is desirable to provide accurate timing of exhaust valve openings and a well-controlled opening rate and extent. To this end, it is advantageous in these systems to apply sharp hydraulic pulses to the slave pistons so that they open the exhaust valves rapidly. In order to both stop the slave pistons' motion and prevent excessive opening of the associated exhaust valves, reset or "clipping" mechanisms are required that reduce the hydraulic fluid pressure when either the hydraulic fluid pressure reaches a predetermined maximum or the slave pistons have reached the end of their desired stroke.
A typical slave piston design incorporating such a reset mechanism uses a hollow lash-adjusting screw containing a reciprocating plunger that makes a face fit over a hole in the slave piston surface. With this design the travel of the reciprocating plunger is arrested upon contact with a press-fit pin that fits in a slot within the body of the plunger. However, this system is relatively costly to manufacture due to the complex configurations of its various parts, the need to test it to ensure that the pin will not come out, etc. The hollow lash-adjusting screw is also a problem because it may break if tightened excessively.
It is therefore an object of the present invention to provide an improved slave piston clipping apparatus. It is a more particular object of this invention to provide slave pistons which are more robust, easier to manufacture and display rapid clipping rates.